Safety System for Deep Water Drilling Units Using a Dual Blow Out Preventer System

ABSTRACT

A dual-BOP or multi-BOP self-standing riser configuration is disclosed, including at least a riser or another similarly fixed tubular structure disposed in communication with an associated drilling vessel and a subsurface well. The system supplements the traditional mud-line level BOP with one or more additional near-surface BOPs, which are tensioned using an adjustable buoyancy chamber rather than by means of a vessel-born tensioning device.

STATEMENT OF RELATED CASES

The present application claims the benefit of prior U.S. provisionalapplication No. 61/330,620 filed May 3, 2010.

BACKGROUND

When drilling in deep water (e.g., greater than 350 ft. water depth), afrequent practice is to employ a mobile offshore drilling unit (MODU). Atypical MODU can be either a semi-submersible drilling unit or a drillship. The common practice for conducting operations is to run a subseablow out preventer (BOP), which uses an associated or containedapparatus called a ram to (i) close around various pipe diameters (piperams); (ii) fully close the well (blind rams); (iii) close around mostpipe diameters (annular rams); or (iv) shear a pipe (shear ram). SuchBOP system assemblies are usually either hydraulically and/orelectrically actuated, with various controls disposed on the MODU, oreven an acoustical activation that can be remotely activated away fromthe rig.

These BOPS are installed on a riser and positioned on the wellhead at ornear the mud line. The riser is generally between 16-inches in diameterto 22-inches in diameter. The riser will usually also carry the controland activation lines from the MODU to the BOPs. The riser is typicallytensioned and held in place by riser tensioners located on the MODU.Such systems have been used by MODUs for years in water depths over10,000 ft.

Other systems, for example, as disclosed in U.S. Pat. No. 7,458,425 toMillheim et al. entitled System & Method of installing & Maintaining anOffshore Exploration & Production System Having an Adjustable BuoyancyChamber show an adjustable buoyancy chamber disposed in communicationwith the riser underwater, so that riser tension can be varied to eitherraise the riser and/or a wellhead above the surface (e.g., forintervention) or lower the riser and wellhead (e.g., for safety during astorm, etc.) either with or without a drilling ship.

A common misconception associated with this configuration is that theriser/BOP assembly is sufficient to establish and maintain control ofthe well by closing it off in the event of a fluid incursion (whetheroil, gas and/or water), and to maintain the integrity of the well bycirculating incurred fluids in water in order to regain control of thewell in an emergency.

However, a recent drilling accident in the Gulf of Mexico demonstratesthat the traditional riser/BOP configuration can fail when hydrocarbons(oil and gas) are uncontrollably released from a well, thereby causingextensive environmental harm and loss of human life. Needless to say,the MODU used in the Gulf of Mexico incident was also destroyed. Thisevent demonstrates that the industry's assumption about the existing BOPriser system, which was previously thought safe and nearly fool-proof,is incorrect and should be challenged.

SUMMARY OF THE INVENTION

A self-standing riser system is provided, said system including at leasta subsurface well disposed in communication with a first BOP; a riserassembly disposed in communication with said subsurface well; anadjustable buoyancy chamber disposed in communication with said riserassembly; and a second BOP disposed in communication with said riserassembly located above said adjustable buoyancy chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a combined riser and BOP configuration according to theprior art.

FIG. 2 depicts an example embodiment of the present invention, includingone or more near-surface BOPs tensioned into place by an associatedadjustable buoyancy chamber.

FIG. 3 depicts the example embodiment of FIG. 2, wherein a drilling shipor MODU is disconnected from the riser and moved away from the wellsite.

FIG. 4 depicts the example embodiment of FIG. 2 as disposed in either afixed or dynamically positioned configuration.

FIG. 5 depicts a diver-accessible, water-proofed chamber disposed incommunication with one or more near-surface BOPs.

FIG. 6 depicts a further example embodiment in which the adjustablebuoyancy chamber has been used to lift the near-surface BOPs to thewater surface for further handling by a MODU or drilling ship.

DETAILED DESCRIPTION OF SEVERAL EXAMPLE EMBODIMENTS

Broadly stated, this disclosure presents a newly designed BOP risersystem in which disadvantages of the prior art are overcome.

Referring to FIG. 1, a prior art BOP riser system is depicted,comprising a riser 1 suspended from a drilling vessel 2, disposed incommunication with a subsurface well 3. Just above the mud line 4, a BOPstack 5 is installed.

As suggested above, this system has many drawbacks. For example, thesubsurface well can not be easily controlled from the surface,especially in deep waters where remote-operated vehicles are required.Also, the BOP must be cooled prior to initiating shutdown of the wellbecause of heat associate with the near-well drilling activity.Moreover, the well can not be quickly closed in during an emergency inthe event of dangerous subsurface conditions. Finally, the drill ship orMODU associated with the site must be quickly decoupled from the riserin order to escape a pending disaster.

As seen in FIG. 2, the present invention improves the prior art bydisposing a riser 1 (noting that the term riser is used flexibly in thiscontext, and is broad enough to encompass the wide variety of risers,stacks, and other concentric or fixed tubular structures used duringdrilling) in communication with an associated drilling vessel 2 and asubsurface well 3 by supplementing at the mud level 4 a BOP stack 5 withone or more additional BOPs 6, tensioned by means of an adjustablebuoyancy chamber 7 rather than by means of a vessel-born tensioner(chains, lifts, etc.).

This self-standing riser BOP configuration has many advantages. Forexample, as seen in FIG. 3, an associated drilling vessel 2 or MODU canbe quickly decoupled from the wellhead (rather than the riser) andremoved from the scene or location of a safety event.

Upper BOP(s) 6 can be quickly closed using a contained ram or the like,without the delay associated with an extensive cool-down period. The ramcan be actuated either electronically or acoustically, etc., or evenmanually by divers just beneath the surface rather than cumbersome ROVsoperating in deep water. This configuration is equally effective withboth fixed-anchor systems (as in FIG. 1) and dynamically positionedriser configurations (see FIG. 4 at 1 and 1′), and a drilling vessel 2can moved be out and replaced with successive vessels appropriate fordifferent tasks (testing, separation, etc.) if desired.

The upper BOP(s) 6 can be used as both a redundant operating system anda redundant safety system. For example, in the case of operations, aneighboring rig can control wellbore fluids at multiple locations (e.g.,the mud line and near the surface). If the mud-level BOP(s) should fail,operations can continue by controlling the near-surface BOP(s).

For safety, a number of BOP(s) disposed at different locations along theriser (again, for example, near the mud line and near the surface) canbe equipped with rams or other shut-offs in order to more easily andquickly control the well during an emergency.

The buoyancy chamber(s) 7 support (either fully or partially) the weightof both the riser and the near-surface BOPs in the event the drillingship or MODU 2 must disconnect and move away from the well. In thismanner, the system maintains the integrity of the riser system until theMODU can return or be replaced with another suitable vessel, which isthen reconnected to the riser for continuing operations.

Another advantage of the instant system is the fact that thenear-surface BOP(s) 6 can also be located in very shallow waters, wherein the event of a component failure or the like, a diver can deploy torepair the BOP(s). This is not possible in the case of most deep-waterBOPs 5.

In fact, recent events associated with a deepwater BOP failure show thatsole dependency on ROVs to repair or reactivate the deepwater BOPs 5 is,in some situations, ineffective, whereas in the presently claimedconfiguration BOP(s) 6 would still be accessible, whether by ROVs,divers or diver-assisted vessels.

A functional improvement to the workability of near-surface BOP(s) 6 forrepair would be the addition of a waterproofed outer hull 8 in whichdivers can enter the chamber, pump out or otherwise evacuate the waterand work in a more favorable environment 9 to repair or reactivate theBOP(s) (see FIG. 5).

This configuration offers other advantages once the riser system hasbeen connected. For example, there are frequently minimal time windowsduring which a BOP assembly will require service or movement. By virtueof the disclosed near-surface BOP arrangements, the system can bequickly closed for service or movement and downtime due to the presenceof loop currents (or other fast-moving currents) otherwise needed toconnect or re-connect the riser system will be minimal, thereby savingmillions of dollars. In contrast, a MODU cannot perform these operationswith the riser under such circumstances.

The dual (or multi) BOP configuration used in combination with anadjustable buoyancy chamber can be used to tension the riser system nearthe surface so that it can be joined in a conventional manner by a MODU(see FIG. 4), and even lift the upper BOPs to the water level or higherfor connection to a drilling ship (see FIG. 6).

The foregoing specification is provided for illustrative purposes only,and is not intended to describe all possible aspects of the presentinvention. Moreover, while the invention has been shown and described indetail with respect to several exemplary embodiments, those of ordinaryskill in the pertinent arts will appreciate that minor changes to thedescription, and various other modifications, omissions and additionsmay also be made without departing from either the spirit or scopethereof.

1. A self-standing riser system, said system comprising: a subsurfacewell disposed in communication with a first BOP; a riser assemblydisposed in communication with said subsurface well; an adjustablebuoyancy chamber disposed in communication with said riser assembly; anda second BOP disposed in communication with said riser assembly locatedabove said adjustable buoyancy chamber.
 2. The system of claim 1,wherein said second BOP is also disposed in communication with a surfacevessel.
 3. The system of claim 1, wherein said first BOP furthercomprises a plurality of BOPs.
 4. The system of claim 1, wherein saidsecond BOP further comprises a plurality of BOPs.
 5. The system of claim1, wherein each of said first BOP and said second BOP further comprise aplurality of BOPs.
 6. The system of claim 1, further comprising awater-proof chamber disposed around said second BOP.
 7. The system ofclaim 1, wherein said adjustable buoyancy chamber is used to tensionsaid riser assembly to a depth at which a human diver can service orreplace said second BOP.
 8. The system of claim 1, wherein saidadjustable buoyancy chamber is used to tension said riser assembly suchthat said second BOP is lifted to approximately the same height as thesurface of a surrounding body of water.
 9. The system of claim 1,wherein said riser system is restrained in place using a fixed anchoringsystem.
 10. The system of claim 1, wherein said riser system ispositioned relative to said wellhead using dynamic positioning.